The present invention relates to a telescopic adjusting crank for adjusting the lift link on a tractor 3-point hitch.
The typical tractor 3-point hitch includes a pair of upper lift arms which are pivoted by a hydraulic cylinder, a pair of lower draft links, and a pair of lift links interconnecting the lift arms and draft links. Typically, one of the lift links is made of adjustable length so as to accommodate leveling of an implement attached to the tractor. The adjustable length lift link will typically include a threaded rod portion and a threaded tubular portion with one of the portions being rotatable through a crank and transmission mechanism so that upon rotation the threads cause the link to vary in length. If the tractor is provided with an operator's cabin, or on large tractors, the spacing between the driver's seat and the adjusting crank is too great for the operator to reach the crank while safely seated in the operator's seat. In these cases it has been known to provide an extension for the crank so that the crank can be positioned closer to the operator. Because of the vertical distance through which the hitch can move, it has also been known to make the crank telescopic so that the upper part of the crank can be in a fixed axial position relative to the operator.
In the known telescopic adjusting cranks for tractor 3-point hitches, the shaft section has been made of hexagonal shape and was formed of a high grade steel. The upper tubular portion of the crank had an interior shape to slidably receive the hexagonal shaft. This structure had the disadvantage of being relatively expensive to manufacture due to the interior shape of the tubular portion. Another disadvantage with this structure was that, when in the extended condition, the hexagonal rod was exposed to the elements and would get dirty and corrode so that when the shaft was moved into the tube it caused erosion of the metal until finally the fit between the parts would no longer transfer the rotation from the tube to the shaft.